Method of making electrical heating units



Feb. 4, 1930. w. A. BRAUN ET AL METHOD OF MAKING ELECTRICAL HEATINGUNITS Original Filed June 10. 1925 2 Sheets-Sheet 6 INVENTORJ M Mymam/Lu, WTWM ATTORNEYS Feb. 4, 1930. w. A. BRAUN El AL 1,745,526

METHOD OF MAKING ELECTRICAL HEATING UNITS Original Filed June 10, 1925 2Sheets-Sheet 2 Fi .3. j

(Kim-W r% A TTORXE Y5:

Patented Feb. 4, 1930 UNITED STATES PATENT OFFICE WILLIAM A. BRAUN ANDCHARLES MAURER, OF DOVER, OHIO, ASSIGNORS TO DOVE MANUFACTURING (30., OFDOVER, OHIO METHOD OF MAKING ELECTRICAL HEATING UNITS Originalapplication filed .Tune 10, 1925, Serial No. 36,128. Divided and thisapplication filed February 10, 1926. Serial No. 87,288.

This invention relates to improvements in methods of'making heatingunits with particular reference to that class of units in which aresistance wire is embedded in a suitable di-electric material within ashallow container which forms a portion of the unit when completed.Common examples of such heat units are to be found in sad irons,vulcanizers and other articles in which the eontainer is necessarily ofhighly conductive material and in. which the resistance wire is locatedin close proximity to the wall of the container but necessarilyelectrically insulated therefrom in such a manner as to avoid shortcircuits. The embedding material must not only be highly di-electricbut'it must also be capable of holding the resistance wire in place andit must possess maximum heat conductivity whereby the heat generated bythe electric current in the wire may be rapidly conveyed and distributedthroughout the wall of the container to be heated.

Heretofore the operation of preparing the resistance wire and insertingit in the embedding material has been a diflicult operation requiringconsiderable time, care and skill on the part of the workmen in order toavoid short circuits between successive loops or portions of the wireand between the wire and the wall of the container. It is the object ofthis invention to provide a more simple and more expeditious method andone which can be practiced by comparatively unskilled employees and inwhich uniform results may be attained, the danger of short circuits beiueliminated and the resistance wire being un ailingly and uniformlyembedded and held in the embedding material in a predetermined spacedrelation of the various portions to each other and to the wall of thecontainer. I

This application is a division of a case heretofore filed by us on orabout J une 10th, 1925, Serial No. 36,128 and relating to apparatuswhereby the method herein claimed may conveniently be practiced.

In the drawin s:

Figure 1 is a pan view of the holding form employed in the practice ofthe improved method as seen from the side at which the resistance wireis applied, and showing a helically coiled resistance wire in positionthereon preparatory to the annealing thereof or theinsertion thereofinto the embedding material. The form illustrated is used in themanufacture of sad irons.

Figure 2 is a sectional view drawn on line 2-2 of Figure 1.

Figure 3 is a similar view showing the form in the position which itoccupies when holding the resistance wire coil in an iron base having arecess partially filled with embedding material.

Figure 4 is a similar view of the sad iron erence characters throughoutthe several views.

In the practice of the improved method a resistance wire of the requiredlength and cross section is first wound into a helical coil '1 of smalldiameter. The diameter of .the coil is preferably about half of thethickness of the layer of embedding material which is to receive it.This coil is then looped or turned upon itself into the position whichit is to occupy when embedded in the container or recessed base, theform of the loops and their position being such as to obtain a desiredheat distribution. Inthe manufacture of sad irons it is desirable to soform the loops that there will be a plurality of portions of the coilextendin along each side in the direction of the point with the endsbrought into proximity in the rear portion and extended upwardly forconnection with the conducting wires of an electric circuit.

The wire is looped in the desired position The holding form is then usedas a carrier to convey the looped coil intoa layer of plastic embeddingmaterial, preferably a material which becomes plastic or semi liquid bythe addition of water, but which tends to harden when dry and which maybe baked in the form of a brick. The holding form is utilized to holdthe coil of wire in its embedded position when the wire embeddingmaterial is being dried or otherwise hardened sufficiently to retain thewire. The form is then withdrawn and an additional layer of semi-liquidor plastic embedding material applied to fill voids and to completelycover the wire. Thereafter the embedding material is again dried,pressed and baked. In the manufacture of sad irons and similar articlesa metallic base is employed which is suitably recessed to receive thelayers of embedding material with the wire therein in spaced relation tothe walls of the base or container and the wire is so positioned orlooped in this recess as to provide the desired heat distribution fiveror throughout the bottom surface of the ase.

Referring to Figure lit will be observed that the helically coiled wireis arranged in loops having portions 1, 2 and 3 extending along onesurface of a dielectric form or plate 4 on each side of the longitudinalcenter of the form. In the rear portion of the form one end of the coilis formed into additional portions 5, 6, 7 and 8 extending back andforth, with the extremity of the coil leading to a tubular stud 9through which the 'uncoiled extremity of the wire passes. On the otherside of the longitudinal center line the other end portion 12 of the rcoil extends to'a tubular stud '15; through which'theuncoiled endportion 10 of the'wire passes. L

The portions .1, 2, 3, 5, 6, 7, 8 and 12 of the wire coil are heldinposition by positioning pegswhich are secured to the platel and arrangedin suitable rows to receive the. coiled wire between them. The pegs ofthe outer row have semi-cylindrical portions 20 and reduced end portions21. The wire coil is received upon the shoulder 22 at the outer end ofthe semi-c lindrical portion 20. The.

flattened sides 0 the semi-cylindrical portion 20 are adapted to fitagainst the side ,wall 25 of the base or container 26 shown in Figure 3when the form is inserted therein for the purpose of positioning thewire and holding it in the layer 27 of embedding material. The pegs inthe inner rows preferably have cylindrical portions 30 correspondingwith the semi-cylindrical portions 20 of the pegs in the outer row andreduced exfrangible and non-combustible under the temperatures to whichthis material is subjected, a composition of lava or of asbestos and.carbon bein preferably employed. The plate 4: is also formed of similarmaterial, the material commercially known as bakelite being preferred,although any other material possessing the necessary rigidity and whichhas a low-co-efiicient of expansion and contraction and which will notwarp or break in ordinary use, may be used.

To facilitate manipulating the form and also to provide means whereby itmay be rigidly secured to the base or container, we preferably providethe plate 4 with a centrally disposed swiveled thumb piece 38' having ascrew threaded end portion which projects into the space between theinner rows of coil holding pegs and which is adapted to be screwed intoa socketed stud 39 formed in afi the recess.

The form 4 is provided with a set of gauge pins 40 having reduced endportions of greater length than those of the pegs heretofore described.These gauge pins 40 are otherwise preferably formed in the same mannerasthe pegs heretofore described, their inner portions being flattened ifin the outer row or cylindrical if in the inner row. They preferablyconstitute a portion of the series of pegs upon which the wire coil issupported.

The use of the form will be readily understood from the abovedescription but will here be briefly reviewed. After forming theresistance wire into a helical coil, except as to the end portions, oneend portion is passed through one of the tubular studs 9 or 15 and thecoil is then looped over the pegs as shown in Figural until its otherunwound end can be passed through the companion tubular stud. Theseunwound ends project from the rear face of the plate 4, i. e., the upperface when the form is in the position in which it is shown in Figure 3.They are connected with electric circuit terminals and electric currentin suficient volume and pressure is passed throu h the wire to heat itto a cherry the current is being passed through the wire. Thereupon theform is adjusted to the container or base as shown inFigure 3, therebycarrying the coil of wire into the recess, said recess having beenpreviously partially filled with semi-liquid or plastic embeddingmaterial. The wire will be embedded therein to a depth which isdetermined by the gauge pins 40, i. e by the length of the reduced endportions of the gauge pins, the shoulders 41 of which are in the sameplane with the shoulders 22 and 22' on all of the-pegs above described.These gauge pins co-operate with the pins of the outer row having theflattened side surfaces 20 to secure an accurate positioning of the coilin the container or ase.

After the holding form has been utilized to embed the resistance wire asshown in Figure 3 it is left in position until the embedding materialhas become suficiently dry and hard to support and retain the wire inthe position in which it has been placed by the form. Thereupon the formis withdrawn, the

' slightly tapered extremities of the pegs permitting a withdrawal ofthe form Without disturbing the wire. The second layer of embeddingmaterial is thereupon applied in a suiiiciently fluid condition to allowit to readily fill the voids heft by pegs in the orig inal layer. Thesecond layer is sufficiently thick to properly cover the coils, portionsof the latter being exposed the upper surface of the original layer.will be noted that the original layer i such thickness and the reducedends "e gauge pins are of such .iength that the thicker portions of thepegs wilt not enter the embedding material. This is desirable to avoidthe displacement extent when the resistance wire is being insorted Afterthe second. layer of embedding mahas been applied it is allowed to dryirden and then compressed preferably in hydraulic press under a pressureof ap proximately forty tons to the square inch, after which thecontainer with the embedding material therein is baked in any suitablemanner.

The embedding material used preferably consists of material similar tothat described in Letters Patent of the United States No. 1,530,228,dated March 17, 1925 forga composite pack for electrical heatingelements. This material when mixed with water may be poured into thecontainers and when dried may be baked in brick form by passing anelectric current through v the wire. The above described pressure isapplied in order to eliminate voids, force the binding material into theinterstices between the grains of fused aluminum oxide to cause saidgrains to form intimate contacts-with the wire and also by shifting thegrains, and pressing them upon each other, to break up the coating filmso bonding material which would otherwise tend to envelope the grains.The binding material has less di.-electric strength than the fusedaluminum oxide grains, and also has less heat conductivity. Therefore,by breaking-up the films of bondin material which would otherwiseenvelope t e grains, the dielectric strength and the heat conductivityof the units is increased.

The pegs are preferably arranged in rows transverse to the portions ofthe coil which they support, and in such proximity that they act inpairs to support associated portions of the coil upon the shoulders 22-and between their reduced extremities, each. of the intermediate pegssupporting two portions of the coil, one on each side of said reducedextremity. The coils are therefore supported in much the same mannerthat they would be supported if mounted in channels or grooves in theface of the supporting form but not as continuously, the transverse rowsof pegs being located in sufiicient proximity to keep the coilsubstantially parallel to the face of the form while allowing a freeflow of the material into the coil from all sides and while causingminimum displacement of embedding material when the projecting portionsof the form or reduced extremities of the pegs enter such material.

It will, of course, be understood that in Figure 5, the press plate asindicated at 45 and the head or platen of the press is indicated at 46,while in Figure 6 the base of the sad iron with the completed heatingunit in the recess thereof is assembled with a cover plate 47 and anouter casing or shell 48 connected by bolts or screws 49 and 50,respecthe embedding material to an unnecessary tively in the ordinarymanner.

lVe claim 1. The improvement in the method of forming heating units,which consists in placing in a container a semi-fluid mixture ofdi-electric material of insufiicient solidity to support and retain aresistance wire in set position, positioning a coil of resistance wireupon a suitable form retaining support within said mixture andsupporting it therein by said suport in predetermined spaced relation tothe walls of the container, solidifying said mixture to a wiresupporting condition and then releasing the wire from said support.

2. The improvement in the method of forming heating units, whichconsists in placing in a container a semialuid mixture of di electricmaterial, positioning a coil of re sistance wire Within said mixtureupon a suitable support for maintaining the wire in set position'and inpredetermined spaced relation to the walls of the container in saidmaterial, solidifying said mixture to a wire supporting condition andthereafter releasing the wire from said support, and applying a cover-(ii-electric material, hardening the material, and thereafter releasingthe element from the form.

13. In the art of forming electrical heating units having a resistanceelement embedded in a body of di-electric material, the improved methodwhich consists in winding the element upon a form in substantially theshape it will be positioned in di-electric material, heating the elementby electrification to eliminate internal strains and permanently fix theloop contours, utilizing said form to embed the wound element insemi-fluid di-electric material, and thereafter releasing the elementfrom the form.

14. In the art of forming electrical heating units having a resistanceelement embedded in a body of di-electric material, the improved methodwhich consists in Winding the element upon a form in substantially thesha e it will be positioned in di-electric materia heating the elementbyelectrification to eliminate internal strains and permanently fix theloop contours, embedding said element upon a form in semi-fluiddi-electric material, hardening the material, and thereafter releasingtheelement from the form.

15. In theart of forming electrical heating unitshaving a resistanceelement embedded in a body of di-electric material, the improved methodWhich consists of the following steps in suitable order: (1) winding aresistance element upon a form having insulating supports tosubstantially the shape it will be 85 positioned in di-electricmaterial, (2) utilizing the form to embed the wound element indi-electric material, (3) electrifying the element, and subsequentlyremoving the supports from the element. WILLIAM A. BRAUN.

CHARLES MAURER.

